Polyurethanes are widely used to provide a durable coating on numerous consumer products requiring abrasion resistance, flexibility, and chemical resistance. Polyurethane coating systems are typically fast curing, have good adhesion to a wide variety of substrates, good leveling properties and are excellent film formers. Polyurethane-type coatings may be applied as clear coats with generally transparent or translucent characteristics, thereby making polyurethane coatings ideal for many different applications and, particularly, to enhance and protect the appearance of products, for instance wood paneling and as furniture. Also, polyurethane coatings may be colored to produce coatings that when properly formulated, have good color fastness, while still providing the qualities of substantial abrasion resistance and chemical resistance. Because of their excellent adhesion, polyurethane coatings are often applied directly to the surface of the product, and do not require a primer coat. Many urethane coatings are applied as reactive oligomers, wherein the oligomers are prepolymers that have unreacted isocyanate groups; Typically, prepolymers are reduced or diluted in an aprotic solvent such as an aromatic solvent (i.e. toluene), a ketone (i.e. methyl ethyl ketone), an ester (i.e. butyl acetate), an ether (i.e. tetrahydrofuran), a tertiary amine (i.e. 1-methyl pyrrolidone), or a mixture thereof. Potentially the isocyanate group can react with the substrate, react with ambient moisture, or with an in situ reactant, forming a cross-linked polymer with excellent abrasion resistance. Most urethane coatings applied to wood or simulated wood surfaces cure through reaction with the ambient moisture. The major advantage of a moisture curing system is that the coating has a long pot life. A potential disadvantage is that the isocyanate group can react with additives in the coating having labile protons (i.e. alcohols, carboxylic acids and most amines). Another disadvantage to moisture-cured urethanes is that the cure time of the coating can vary significantly depending on the ambient conditions, and this uncertainty makes it difficult to execute a production schedule. Variable cure times can also affect how much of the coating remains on the surfaces of the substrate, and can necessitate in an additional coating. The major disadvantage to urethane oligomers is that they cure through an isocyanate functional group, and airborne isocyanates are extremely toxic. Typical exposure limits (TLV) are in the parts per billion range, and heated air ovens generally create air borne isocyanates which must be environmentally treated.
A preferable coating is one that has a long pot life, yet could be cured to a highly cross-linked state virtually instantaneously. It would be further preferable if the coating could be cured with very little heat. A further preference is that the coating can be applied at very high solids, with a target of 100% solids, so as to eliminate the removal and disposal of solvent. A most important consideration is that the coatings not cure through an isocyanate group, but via another moiety that is lower in toxicity.
Wood surfaces, such as hardwood flooring, furniture used in office, residential, health care and hospitality environments, and cabinetry are ideally suited for coating with polyurethanes in order to protect the surfaces from abrasion and to provide chemical resistance. Furthermore, synthetic or natural surfaces and ceramics can be enhanced by such a coating.
Furniture and other wood products are under constant exposure to bacteria, fungi and microbes that exist in their respective environments. For example, polyurethane coated flooring, cabinetry, and furniture are particularly susceptible to bacteriological and other microbial development. People and moveable objects, both of which are carriers of bacteria and microbes, account for the majority of microbes on the flooring of heavily trafficked areas. The traffic results in a continual deposit of bacteria and microbes on the floorings, and consequently there develops a “bioburden” which is a continuous source for cross-contamination. Additionally, polyurethane coated cabinetry and surfaces found in bathrooms and kitchens, whether incorporated in domestic settings or commercial settings, produce a bioburden as a consequence of being in contact with contaminated parts of the body. Residual microbes typically remain and continue to populate the coated flooring, cabinetry, furniture, and other surfaces.
The net effect is that there are created a variety of environments which are a constant source of bacterial, fungal or other microbial contamination. Not only are polyurethane coated products contaminated by the bacteria, fungi and microbes in these environments, but these environments also aid in the proliferation of the bacteria, fungi and microbes. The presence of humidity or moisture in these environments is generally conducive to the growth of bacteria, fungi and microbes. Bacteria, fungi and microbes can grow and multiply on the surfaces of the coated products, producing significant levels of contamination, in the form of a bioburden. If left unchecked, the bioburden builds over time.
To counter the presence and growth of microbes on the surface of polyurethane coated products, a disinfectant or sanitizing agent is typically applied to the surface, such as by washing, spraying or wiping. Unfortunately, disinfectants and sanitizing agents are not always properly applied and thus not always completely effective. In any case, topically applied disinfectants and sanitizing agents provide only temporary removal of the microbes on the surface because, as previously mentioned, the associated environment is a source for further contamination. Reapplication of the disinfectant and sanitizing agent is costly, time consuming, non-durable, and therefore only temporarily controls the presence and growth of microbes.
Furthermore, non-thorough cleaning of the polyurethane coated products leaves residual contamination as previously mentioned. Without attention to detail when cleaning the coated products, residual contamination is more likely to exist. Additionally, by applying the disinfectant or other biocide to the surface of the coated product, a residual of the disinfectant or biocide enters the environment and may negatively impact the environment.
What is needed is an antimicrobial agent that can be incorporated, or embedded, into a polymeric coating prior to polymerization, where that antimicrobial agent survives polymerization. In particular, what is needed is an antimicrobial agent incorporated into a polymeric coating that is applied to surfaces, and that is free from toxic effects and is durable over the lifespan of the polymer coating. Further needed is a polymeric coating having at least one antimicrobial agent incorporated in the polymeric coating where the antimicrobial agent will migrate to the surface of the polymeric coating as needed to provide appropriate protection. Further needed is a polymeric coating having antimicrobial properties that may be applied by conventional coating techniques. Further needed is a polymeric coating having antimicrobial compounds or chemicals incorporated in the polymeric coating, wherein the addition of the antimicrobial compounds or chemicals has no deleterious effect on the properties of the coating, so that the mechanical and physical properties remain unaffected.
And further still, it is desired that the coating be applied at substantially 100% solids, and that the coating is a urethane coating or a similar coating having durable antimicrobial properties with good efficacy.
There have been some reported successes in medicinal chemistry of the preparation of antimicrobial film coatings using urethane acrylates in combination with antimicrobial agents. Greff et al., U.S. Pat. No. 6,102,205 discloses a polyvinylpyrrolidone iodine complex (e.g. PVP-I2), which is admixed with a urethane acrylate prepolymer and a photoinitiator system that initiates polymerization in visible light, forming an antimicrobially effective film. The antimicrobially effective film is biocompatible with mammalian skin.
There is some prior art concerned with flooring and other wood or simulated wood surfaces utilizing radiation curable urethane acrylates, such as Ehrhart et al, U.S. Pat. No. 5,003,026, but these coatings are substantially concerned with gloss, wear and stain resistance. Erhart'026 discloses several urethane acrylate oligomers that are suitable for wood coating.
A major manufacturer of urethane acrylic oligomers is Sartomer Technologies Co, Inc., of Exton Pa., and inventors Ceska et al., U.S. Pat. No. 6,399,672, discloses radiation curable coating compositions, where the compositions can be formulated to cure by microwave, UV or electron beam radiation. These forms of radiation are also known to have sterilization properties, and Ceska'672 notes that coatings cured using this technology would be useful for flooring and can (as in canned goods) coatings. Ceska'672 does not teach the utility of adding antimicrobial agents.
Berg et al., U.S. Pat. No. 6,096,383, discloses a process for applying a coating to a floor surface and curing that coating with UV radiation. The source of UV radiation is mounted on the front of a self-powered vehicle.